Piston sealing ring assembly having a gap cover element

ABSTRACT

The present disclosure provides a sealing ring assembly having a ring and one or more gap cover elements, configured to seal a high-pressure region from a lower pressure region of a piston and cylinder device. The ring may be segmented, and the gap cover elements may engage with interfaces between the ring segments. The gap cover elements are configured to move radially outward and wear as the ring wears. The gap cover elements may include, for example, wedge-shaped features that engage with corresponding wedge recesses in the interfaces. The sealing ring assembly may include a high-pressure boundary and a low-pressure boundary. As the sealing ring wears, the gap cover elements stay engaged with the interfaces, so that ring gaps do not form on the low pressure boundary.

The present disclosure is directed towards a piston sealing ringassembly and, more particularly, the present disclosure is directedtowards a piston sealing ring assembly that includes a gap cover elementthat maintains a seal as a sealing ring assembly wears. This applicationclaims the benefit of U.S. Provisional Patent Application Nos.62/543,299 filed Aug. 9, 2017, and 62/543,296 filed Aug. 9, 2017, thedisclosures of which are hereby incorporated by reference herein intheir entirety.

BACKGROUND

In some circumstances, it is desirable for a seal to function for aslong as possible before needing replacement (e.g., a long maintenanceinterval). For example, a typical target may be hundreds or thousands ofhours of operation. Throughout these run-hours, the seal may wear downin the radial direction. To compensate for the radial wear, the seal maybe split into one or more ring segments, allowing pressure to expand thering segments outward and maintain sealing contact with the cylinderwall in spite of material removed via wear. For example, the totalcircumferential arc length of the resulting gaps between ring segmentsopens by 2*pi*ΔR, where ΔR is the radial wear of the seal. If, forexample, a self-lubricating material is used for the seal, in which wearrates can be relatively higher than those of traditional oil-lubricatedseals, the gap may open by an amount that results in an unacceptableleakage flow. This leakage limits the performance, and thus effectiveoperating life, of the seal.

Additionally, if the ring gaps are covered from the front (i.e., highpressure region) and open to the rear of the seal (i.e., low pressureregion), and are therefore at low pressure relative to the front of theseal, a large bending stress may result in the front cover ring becausethe front ring spans the gap in the rear ring. The bending stress in thefront part may increase dramatically as the gap width gets larger (e.g.,as the seal wears).

SUMMARY

In some embodiments, the present disclosure is directed to a sealingring assembly. The sealing ring assembly includes a ring and a gap coverelement. The ring includes a first end face and a second end facedefining an interface. At least one of the first and second end faces atleast partially faces radially inward. The ring is configured to causethe interface to widen as the ring wears. The gap cover element isconfigured to form a seal against the first and second end faces. Thegap cover element is further configured to move radially outward tomaintain the seal as the interface widens.

In some embodiments, the ring includes a radially outer surfaceconfigured to seal against a bore and the gap cover element comprises aradially outer surface configured to seal against the bore as the ringwears. As the interface widens, at least some of the radially outersurface of the gap cover element is configured to widen.

In some embodiments, the first and second end faces form a wedge-shapedrecess and the gap cover element includes a wedge configured to engagewith the wedge-shaped recess.

In some embodiments, the ring includes a back face configured to be incontact with a low-pressure region, and the gap cover element isconfigured to form the seal with the first and second end faces adjacentto the back face.

In some embodiments, the ring is a first ring, and the sealing ringassembly includes a second ring. The second ring includes at least onering segment arranged axially adjacent to the first ring and configuredto seal axially against the first ring and against the gap coverelement.

In some embodiments, at least one of the ring and the one gap coverelement are made at last in part of a respective self-lubricatingmaterial.

In some embodiments, the ring and the gap cover element are configuredfor oil-less operation.

In some embodiments, the interface is a first interface, the gap coverelement is a first gap cover element, and the ring includes a third endface and a fourth end face defining a second interface. Each of thethird and fourth end faces at least partially face radially inward, andthe ring is configured to cause the second interface to widen as thering wears. The sealing ring assembly includes a second gap coverelement configured to form a second seal against the third and fourthend faces and the second gap cover element is configured to moveradially outward to maintain the second seal as the second interfacewidens.

In some embodiments, the ring includes at least two ring segments.

In some embodiments, the ring includes a first axial end face and asecond axial end face further defining the interface, and the gap coverelement is further configured to seal against the first and second axialend faces.

In some embodiments, the at least one of the first and second end facesincludes an azimuthal component and a radial component. For example, theat least one face may include a face at an angle to the radialdirection.

In some embodiments, the present disclosure is directed to a pistonassembly. The piston assembly includes a piston having a circumferentialgroove that extends around an outer surface of the piston, and a sealingring assembly arranged in the circumferential groove.

In some embodiments, the present disclosure is directed to a deviceincluding a cylinder, a piston and a sealing ring assembly. The cylinderincludes a bore, the piston includes a circumferential groove thatextends around an outer surface of the piston, and the piston isconfigured to translate axially in the bore. The sealing ring assemblyis arranged in the circumferential groove, and the sealing ring assemblyis configured to seal against the bore.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The drawings are provided for purposes of illustration only andmerely depict typical or example embodiments. These drawings areprovided to facilitate an understanding of the concepts disclosed hereinand shall not be considered limiting of the breadth, scope, orapplicability of these concepts. It should be noted that for clarity andease of illustration these drawings are not necessarily made to scale.

FIG. 1 shows a cross-sectional end view of a portion of an illustrativepiston and cylinder assembly;

FIG. 2 shows a perspective view of a portion of an illustrative pistonassembly;

FIG. 3 shows a side view of a portion of an illustrative seal ringassembly;

FIG. 4 shows a view of the rear face of an illustrative sealing ringassembly at a new or low wear condition, in accordance with someembodiments of the present disclosure;

FIG. 5 shows a view of the rear face of an illustrative sealing ringassembly at a high wear condition, in accordance with some embodimentsof the present disclosure;

FIG. 6 shows a view of the rear face of an illustrative sealing ringassembly at an intermediate wear condition, in accordance with someembodiments of the present disclosure;

FIG. 7 shows a view of the front face of an illustrative sealing ringassembly at a new or low wear condition, with a gap cover elementremoved, in accordance with some embodiments of the present disclosure;

FIG. 8 shows a view of the rear face of an illustrative sealing ringassembly at a new or low wear condition, with a gap cover elementremoved, in accordance with some embodiments of the present disclosure;

FIG. 9 shows a view of the rear face of an illustrative sealing ringassembly at a new or low wear condition, in accordance with someembodiments of the present disclosure;

FIG. 10 shows a view of the rear face of an illustrative sealing ringassembly at a high wear condition, in accordance with some embodimentsof the present disclosure;

FIG. 11 shows a view of the rear face of an illustrative sealing ringassembly at an intermediate wear condition, in accordance with someembodiments of the present disclosure;

FIG. 12 shows a view of the front face of an illustrative sealing ringassembly at a new or low wear condition, with a second ring segmentremoved, in accordance with some embodiments of the present disclosure;

FIG. 13 shows a view of the rear face of an illustrative sealing ringassembly at a new or low wear condition, with a second ring segmentremoved, in accordance with some embodiments of the present disclosure;

FIG. 14 shows a view of the rear face of an illustrative sealing ringassembly at a new or low wear condition, in accordance with someembodiments of the present disclosure;

FIG. 15 shows a view of the rear face of an illustrative sealing ringassembly at a high wear condition, in accordance with some embodimentsof the present disclosure;

FIG. 16 shows a view of the rear face of an illustrative sealing ringassembly at an intermediate wear condition, in accordance with someembodiments of the present disclosure;

FIG. 17 shows a view of the front face of an illustrative sealing ringassembly at a new or low wear condition, with a ring segment removed, inaccordance with some embodiments of the present disclosure;

FIG. 18 shows a view of the rear face of an illustrative sealing ringassembly at a new or low wear condition, with a ring segment removed, inaccordance with some embodiments of the present disclosure;

FIG. 19 shows an illustrative piston assembly including a sealing ringassembly in accordance with some embodiments of the present disclosure;

FIG. 20 shows a cross section view of an illustrative piston andcylinder assembly including a sealing ring assembly in accordance withsome embodiments of the present disclosure;

FIG. 21 shows a cross section view of an illustrative engine includingtwo piston assemblies, that each include a sealing ring assembly inaccordance with some embodiments of the present disclosure;

FIG. 22 shows an exploded perspective view of an illustrative sealingring assembly, in accordance with some embodiments of the presentdisclosure; and

FIG. 23 shows a cross-sectional view of a portion of an illustrativepiston, with a sealing ring assembly disassembled, in accordance withsome embodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure describes a seal for sealing a gas in a pistonand cylinder device, for example, in in the absence of lubricating oil.For example, the seal may include a sealing ring assembly which may beconfigured to travel with the piston, sealing between the piston and abore of the cylinder. Piston and cylinder devices include, for example,engines, gas compressors, and liquid pumps.

The present disclosure provides a sealing ring assembly having geometricfeatures for eliminating gaps between ring segments and correspondinggap cover elements on a low-pressure boundary in the sealing ringassembly, even in the case of very large amounts of radial wear.Accordingly, the sealing ring assembly maintains low leakage andmitigates increased stress at ring gaps, throughout the life ofoperation of the seal.

In the absence of lubricating oil, a sealing ring assembly may beconstructed from a self-lubricating material such as, for example, apolymer or graphite. The use of a self-lubricating material for the sealring assembly may aid in eliminating scuffing or galling failures butmay also result in a relatively high wear rate as compared to aconventional oil-lubricated seal arrangement in which the seal isconstructed of a hard, wear-resistant material (e.g., metal). In somecircumstances, higher wear is inherent to the nature of theself-lubricating material, as it transfers material to the counter-face(e.g., a bore of the cylinder) to form a lubricant film.

The term “seal” as used herein, refers to the creation, maintenance, orboth of a high-pressure region and a low-pressure region. For example, aseal may include a sealing ring assembly that is configured to reduce aleakage rate of gas from a high-pressure region to a low-pressureregion, by limiting flow between a high-pressure boundary and alow-pressure boundary of the seal. Accordingly, a seal can be defined interms of its constraints on a leakage rate. It will be understood that aseal, such as a sealing ring assembly, as described herein, may have anysuitable corresponding leakage rate. For example, in some circumstances,a relatively worse seal may allow more leakage, but may be acceptablebased on one or more relevant performance criterion. In a furtherexample, a sealing ring assembly configured for high efficiencyoperation of a piston and cylinder device may have a relatively lowleakage rate (e.g., be a more effective seal).

As used herein, a “ring segment” shall refer to a sealing elementextending for an azimuthal angle greater than zero degrees, having aradially outer surface, and configured to seal at least along a portionof the radially outer surface against a bore. A ring segment may includeend faces, if not azimuthally contiguous around the full bore.

As used herein, a “ring” shall refer to a sealing element including atleast one ring segment, which may be, but need not be, azimuthallycontiguous along a bore. For example, a ring may include one ringsegment, in which case these terms overlap. In a further example, a ringmay include four ring segments, in which case the ring refers to thecollective of the four ring segments. A ring may include, but need notinclude, one or more interfaces between one or more ring segments. A“ring” shall also refer to a sealing element including at least one ringsegment configured to seal against a land of a piston.

As used herein, a “gap cover element” shall refer to a sealing elementconfigured to seal against one or more ring segments at an interface,and to seal against at least a portion of a bore during wear of the oneor more ring segments. While a gap cover element may function as a ringsegment as the ring wears, for purposes of the discussion in the presentdisclosure, a gap cover element is not considered to be a ring segmentfor purposes of clarity.

As used herein, a “sealing ring assembly” shall refer to an assembly ofone or more rings, and sometimes also one or more gap covers elements,configured to engage with a piston and configured to seal between ahigh-pressure region and a low-pressure region of a cylinder. Forexample, a single ring segment may be a ring and a sealing ringassembly. In a further example, several ring segments and correspondinggap covers may be a sealing ring assembly.

As used herein, a “pressure-locking feature” shall refer to a featureincluded in at least one component of a sealing ring assembly thatprovides pressure locking functionality. As used herein,“pressure-locking” shall refer to the action of causing a resultantforce on one or more components of a sealing ring assembly to maintain(or otherwise control) a relative geometric relationship betweencomponents of the sealing ring assembly, apply a force pushingcomponents of the sealing ring assembly together, or both, duringoperation. The action of differential pressure across a sealing elementmay cause a resultant force that helps maintain the relative geometricrelationship. For example, a pressure-locking feature may include arecess in one or more mating surfaces of one or more sealing elementsthat is open to a low-pressure region but sealed from a high-pressureregion. In a further example, a pressure locking feature may include ageometric shape, arrangement, or both, that causes pressure forces tomaintain a relative geometric relationship among sealing elements.

FIG. 1 shows a cross-sectional perspective view of a portion of anillustrative piston and cylinder assembly 100. Seal 102 is configured toseal between piston assembly 106 and cylinder 104, as piston assembly106 moves axially in cylinder 104. After some amount of wear, as shownby cylinder assembly 110 of FIG. 1A, seal 112 exhibits a significant gap118, which may serve as a leak path.

FIG. 2 shows a perspective view of a portion of illustrative pistonassembly 130. Shown in FIG. 2 is leak path 140 of relativelyhigh-pressure gas 142 past worn seal 134, arranged on piston 132, to aregion of relatively lower pressure 144.

FIG. 3 shows a side view of a seal 160, and gap 152 that has opened asseal 160 wears. Ring segment 162 spans gap 152 in ring segment 164, andexperiences high gas pressure (e.g., during the high-pressure portion ofan engine cycle or air compression cycle) at one boundary, and low gaspressure (e.g., open to atmosphere or near atmospheric conditions). Theresulting stress from the pressure forces may increase as gap 152increases, making ring segment 162 more susceptible to breakage. Ringbreakage may result in further gaps being formed, or destruction ofgeometrical constraints, or both, which may result in high leakage ofgas from, for example, a high-pressure region to a low-pressure region.

The following description of FIGS. 4-21 includes description ofillustrative sealing ring assemblies that may be, in some embodiments,configured to address at least one of the formation of gaps between ringsegments and corresponding gap cover elements with increased wear, andthe formation of high stress areas due to gaps forming as the sealingring assemblies wear.

FIG. 4 shows a view of the rear face of an illustrative sealing ringassembly 200 at a new or low wear condition, in accordance with someembodiments of the present disclosure. Sealing ring assembly 200includes ring segments 202, 204, 206, and 208 (e.g., collectively a“ring”), as well as gap cover elements 212, 214, 216, and 218. Sealingring assembly 200 includes four ring segments and four gap coverelements, although any suitable number of ring segments andcorresponding gap cover elements may be used in accordance with thepresent disclosure. Ring segments 202, 204, 206, 208 may also bedescribed as a ring that has four radial splits, splitting the ring intofour ring segments (e.g., ring segments 202, 204, 206, and 208) in thisillustrative example.

FIG. 5 shows a view of the rear face of an illustrative sealing ringassembly 230 at a high wear condition, in accordance with someembodiments of the present disclosure. Sealing ring assembly 230includes ring segments 232, 234, 236, and 238, as well as gap coverelements 242, 244, 246, and 248. Sealing ring assembly 230illustratively corresponds to sealing ring assembly 200 after undergoinghigh wear (e.g., ring segment 236 corresponds to ring segment 206 afterundergoing a high amount of wear).

FIG. 6 shows a view of the rear face of an illustrative sealing ringassembly 260 at an intermediate wear condition, in accordance with someembodiments of the present disclosure. Sealing ring assembly 260includes ring segments 262, 264, 266, and 268, as well as gap coverelements 272, 274, 276, and 278. Sealing ring assembly 260illustratively corresponds to sealing ring assembly 200 after undergoingrelatively less wear than sealing ring assembly 230 (e.g., ring segment266 corresponds to ring segment 206 after undergoing an intermediateamount of wear).

The following discussion in the context of FIGS. 4-6 describes sealingring assemblies, behavior thereof, and wear thereof. For purposes ofdiscussion, FIGS. 4-6 may be described as views of an illustrativesealing ring assembly at different stages of wear life. Accordingly, forpurposes of clarity, any of FIGS. 4-6 may be referenced to describefeatures of an illustrative sealing ring assembly. Geometricaldirections are referred to herein in terms of cylindrical coordinatesfor simplicity (e.g., X is the axial direction, R is the radialdirection and 0 is the azimuthal direction, as shown in FIG. 4). It willalso be understood that any of sealing ring assemblies 200, 230, and 260may represent a sealing ring assembly in a new (i.e., unworn) condition.For example, a sealing ring assembly may be newly created resemblingsealing ring assembly 230 (e.g., with significant gaps between ringsegments on a high-pressure boundary).

The splits between ring segments 202, 204, 206, and 208 may allowmovement of the ring segments radially outward to maintain sealingcontact with the inner surface of the bore of a cylinder as ringmaterial is removed via wear. Sealing ring assembly 200 may be energizedradially outward against the cylinder bore by the presence of gaspressure (e.g., from a relatively high-pressure region during an enginecycle or air compression cycle) on one or more inner surfaces of sealingring assembly 200. Sealing ring assembly 200 may be energized radiallyoutward against the cylinder bore by a spring on one or more innersurfaces of sealing ring assembly 200.

Sealing ring assembly 200 includes four interfaces between adjacent ringsegments. For example, there are respective interfaces between ringsegments 202 and 204, ring segments 204 and 206, ring segments 206 and208, and ring segments 208 and 202. An interface, as used herein,includes any space between the ends of adjacent ring segments, andcontact points between adjacent ring segments, and, to the extent thereare features that engage with a gap cover element, such features areconsidered part of the interface as well. The interfaces of sealing ringassembly 200 include respective wedge recesses located on the rear faceof sealing ring assembly 200, centered at each of the interfaces. Forexample, interface 280 of FIG. 6 shows the interface between ringsegments 262 and 264. A wedge recess is, for example, the space wheregap cover element 212, which is wedge-shaped, fits, as shownillustratively in FIG. 4. As shown in FIGS. 4-6, the wedge recesses eachextend through the entire radial section of the corresponding ringsegments (e.g., from radially inward surface through radially outwardsurface). The axially-front face, also referred to as the “front face,”of the wedge recesses is nominally a flat plane perpendicular to theaxis of the ring (e.g., along direction X in FIG. 4). For example, wedgerecess front face 237 is shown in FIG. 5. As shown in FIGS. 5 and 6, thesides of the wedge recesses are symmetric about a plane passing throughthe center of the radial split in the ring.

The sides of the wedge (e.g., gap cover element 212) need not besymmetric, but are shown symmetric for clarity. The sides together forman included angle (e.g., included angle 239 in FIG. 5 is a wedge angleformed by gap cover element 236) that is widest at the radially inwardsurface of the ring and narrowest at the radially outward surface. Theincluded angle may be a design parameter and may include any suitableangle such that the radially inward surface of the ring is wider thanthe radially outward surface. For example, in some embodiments, theincluded angle may vary between about 30 degrees and about 150 degrees.The included angle may depend on material properties (e.g., friction,fracture resistance), operating conditions (e.g., peak pressure in ahigh-pressure region, piston speed, engine frequency), bore conditions,fabricating preferences, installation preferences, any other suitablefactors, or any combination thereof.

The term wedge, as used herein, refers to a solid having at least twofaces that meet, or would meet if the wedge is truncated at the point,at an angle between (and not including) 0 and 180 degrees. A wedgeincludes a wide end and a narrow end. The faces that angle towards oneanother from the wide end to the narrow end are termed wedge surfaces.For example, gap cover element 212 is wedge shaped, and may be termed awedge herein. The narrow end of gap cover element 212 is radiallyoutward, and the wide end is radially inward. For example, wedge recesssurfaces 235 of ring segments 236 and 238 engage with correspondingwedge surfaces of gap cover element 246 to create a seal (e.g.,configured to restrict gas leakage). A gap cover element may alsoinclude a wedge feature (e.g., gap cover element 612 of FIG. 14), alongwith non-wedge geometry (e.g., the curved portion of gap cover element612 that resembles a ring segment). It will be understood that thepresent disclosure is described herein primarily in the context of awedge-shaped gap cover element for purposes of brevity and clarity andnot by way of limitation. Any suitably shaped gap cover element, orcombination of differently shaped gap cover elements, may be usedaccording to the general teachings of the present disclosure. Forexample, a sealing ring assembly may include ring segments that are thesame or different and may include gap cover elements that are the sameor different.

Gap cover elements 212, 214, 216, and 218 are wedge shaped, and fit intocorresponding wedge recesses in interfaces between adjacent ringsegments (e.g., ring segments 202 and 204). Gap cover elements fittedinto each of the corresponding recesses, may form a closed seal with nosignificant gaps (e.g., thus restricting gas leakage). As the componentsof sealing ring assembly 200 wear, they may wear-in with adjacentcomponents to form, and maintain, a more complete seal. Gap coverelements 212, 214, 216, and 218 are acted upon by gas pressure on theradially inner surface, exerting a force radially outward, in the samemanner as the corresponding ring segments. For example, during highpressure portions of an engine cycle or air compressor cycle, high gaspressure may act on the radially inner surfaces of gap cover elements212, 214, 216, and 218. This high gas pressure forces the angled sidesof each gap cover element against the corresponding angled sides of thecorresponding wedge recess, creating a seal against radial gas leakagethrough the split in the ring. Also, when acted on by high gas pressureat the radially inward surface, the radially outward surface of thewedge-shaped gap cover element presses against the inner surface of thecylinder (e.g., the bore), forming a seal against axial leakage throughthe split, past the sealing ring assembly.

In some embodiments, sealing ring assembly 200 may be include asolid-lubricant material such as, for example, graphite. For example, aring may be machined from graphite, and split into ring segments 202,204, 206, 208. In a further example, ring segments 202, 204, 206, and208 may be machined as separate parts. In another further example, gapcover elements 212, 214, 216, and 218 may be machined from graphite asseparate parts. In another example, ring assembly 200 may be machinedfrom graphite as a single ring, and then further machined (e.g., wire orlaser cut) into ring segments 202, 204, 206, and 208 and into gap coverelements 212, 214, 216, and 218.

As ring segments 202, 204, 206, and 208 wear they move outward and thesplits open wider (e.g., shown illustratively by corresponding ringsegments 232, 234, 236, and 238). Gap cover elements 212, 214, 216, and218 are pressed outward by gas pressure, and wear in the radialdirection while being supported by the angled sides of the respectivewedge recess. Accordingly, the wear rate of the gap cover element may beself-adjusting to maintain contact with both the angled sides of thewedge recess and the cylinder inner surface (e.g., the bore). In somecircumstances, gap cover elements may wear at a faster rate thancorresponding ring segments, and the wear rate may depend on the wedgeangle. Because the gap cover elements maintain contact with the angledsides of the respective wedge recesses, as well as the bore, sealingperformance may be maintained throughout the life of operation (e.g., asthe sealing ring assembly wears). Further, there are no significant gapsbetween the ring segments and corresponding gap cover elements exposedto a low-pressure boundary of the sealing ring assembly. Each ringsegment is supported everywhere either by pressure or by the wedge,avoiding the stress scenario described in the context of FIG. 3. As thesealing ring assembly wears, the at least one gap cover elementcorrespondingly wears to prevent a substantial ring gap between the ringsegments and the corresponding gap cover element from forming on thelow-pressure boundary of the sealing ring assembly. A ring gap between awedge and wedge recess may also be prevented on a low-pressure boundaryof a sealing assembly.

FIG. 7 shows a view of the front face of illustrative sealing ringassembly 300 at a new or low wear condition, with gap cover element 312removed, in accordance with some embodiments of the present disclosure.Illustrative sealing ring assembly 300, as shown, is similar to sealingring assembly 200, for example. FIG. 8 shows a view of the rear face ofillustrative sealing ring assembly 300 at a new or low wear condition,with gap cover element 312 removed, in accordance with some embodimentsof the present disclosure. Gap cover element 314 is shown in place, forreference. Interface 320 refers to the spatial region where ringsegments 302 and 308 meet. Interface 320 includes a wedge recess, aswell as the split between ring segments 302 and 308, where they touch orvery nearly touch (e.g., at the front face of the sealing ringassembly). Gap cover element 312 includes wedge surfaces 313 and 315,for example, which may engage corresponding wedge recess surfaces whengap cover element 312 is arranged in place in the interface of ringsegments 302 and 304.

FIG. 9 shows a view of the rear face of an illustrative sealing ringassembly 400 at a new or low wear condition, in accordance with someembodiments of the present disclosure. Sealing ring assembly 400includes first ring segments 402, 404, 406, and 408, second ringsegments 403, 405, 407, and 409, as well as gap cover elements 412, 414,416, and 418. Sealing ring assembly 400 includes four first ringsegments, four second ring segments, and four gap cover elements,although any suitable number of first ring segments, second ringsegments, and corresponding gap cover elements may be used in accordancewith the present disclosure. First ring segments 402, 404, 406, and 408may also be described as a first ring that has four radial splits,splitting the first ring into four first ring segments (e.g., first ringsegments 402, 404, 406, and 408) in this illustrative example.

FIG. 10 shows a view of the rear face of an illustrative sealing ringassembly 430 at a high wear condition, in accordance with someembodiments of the present disclosure. Sealing ring assembly 430includes first ring segments 432, 434, 436, and 438, second ringsegments 433, 435, 437, and 439, as well as gap cover elements 442, 444,446, and 448. Sealing ring assembly 430 illustratively corresponds tosealing ring assembly 400 after undergoing high wear (e.g., first ringsegment 436 corresponds to first ring segment 406 after undergoing highwear).

FIG. 11 shows a view of the rear face of an illustrative sealing ringassembly 460 at an intermediate wear condition, in accordance with someembodiments of the present disclosure. Sealing ring assembly 460includes first ring segments 462, 464, 466, and 468, second ringsegments 463, 465, 467, and 469, as well as gap cover elements 472, 474,476, and 478. Sealing ring assembly 460 illustratively corresponds tosealing ring assembly 400 after undergoing less wear than sealing ringassembly 430 (e.g., first ring segment 466 corresponds to first ringsegment 406 after undergoing intermediate wear).

The following discussion is described in the context of FIGS. 9-11 todescribe the sealing ring assembly, behavior thereof, and wear thereof.For purposes of discussion, FIGS. 9-11 may be described as views of anillustrative sealing ring assembly at different stages of wear life.Accordingly, for purposes of clarity any of FIGS. 9-11 may be referencedto describe features of an illustrative sealing ring assembly.Geometrical directions are referred to herein in terms of cylindricalcoordinates for simplicity (e.g., X is the axial direction, R is theradial direction and θ is the azimuthal direction, as shown in FIG. 9).It will also be understood that any of sealing ring assemblies 400, 430,and 460 may represent a sealing ring assembly in a new condition. Forexample, a sealing ring assembly may be newly created resembling sealingring assembly 430 (e.g., with significant gaps between second ringsegments on a high-pressure boundary).

The splits between first ring segments 402, 404, 406, and 408 may allowmovement of the first ring segments radially outward to maintain sealingcontact with the inner surface of the bore of a cylinder as ringmaterial is removed via wear. Sealing ring assembly 400 may be energizedradially outward against the cylinder bore by the presence of gaspressure (e.g., from a relatively high-pressure portion of an enginecycle or air compression cycle) on the inner surface of the sealing ringassembly.

Sealing ring assembly 400 includes four interfaces between adjacentfirst ring segments. For example, there are respective interfacesbetween ring segments 402 and 404, ring segments 404 and 406, ringsegments 406 and 408, and ring segments 408 and 402. The interfaces ofsealing ring assembly 400 include respective wedge recesses, centered ateach of the interfaces. A wedge recess is, for example, the space wherewedge-shaped gap cover element 412 fits, as shown in FIG. 9. As shown inFIGS. 9-11, the wedge recesses each extend through the entire radialsection (e.g., from radially inward surface through radially outwardsurface), and the entire axial section of the corresponding first ringsegments (e.g., from the respective front faces to the respective backfaces of the second ring segments). As shown in FIGS. 10 and 11, thesides of the wedge recesses are symmetric about a plane passing throughthe center of the radial split in the first ring, however the sides neednot be symmetric.

Gap cover elements 412, 414, 416, and 418 are wedge shaped, and fit intocorresponding wedge recesses formed in interfaces between adjacent firstring segments (e.g., ring segments 402 and 404). Wedge shaped gap coverelements 412, 414, 416, and 418 may be acted upon by gas pressure on theradially inner surface, exerting a force radially outward. For example,during high pressure portions of an engine cycle or air compressorcycle, high gas pressure may act on the radially inner surfaces of gapcover elements 412, 414, 416, and 418. This high gas pressure forces theangled sides of each gap cover element against the correspondinglyangled sides of the wedge recess, creating a seal against radial gasleakage through the split. Also, when acted on by high gas pressure atthe radially inward surface, the radially outward surface of the gapcover element presses against the inner surface of the cylinder (e.g.,the bore), forming a seal against axial leakage through the split, pastthe sealing ring assembly.

Second ring segments 403, 405, 407, and 409 are arranged axially forwardof first ring segments 402, 404, 406, and 408, centered at therespective interfaces of the first ring segments. As sealing ringassembly 400 wears, second ring segments 403, 405, 407, and 409 assistsealing near the interfaces, so that if any gaps start to form at theinterfaces near the gap cover elements (e.g., from first ring segmentsmoving out of round, or other configurational changes), the gaps remainsealed by the first ring segments.

In some embodiments, sealing ring assembly 400 is a pressure lockedassembly based at least in part on the high-pressure boundary, and basedat least in part on the low-pressure boundary. Pressure locking refersto the behavior of the sealing ring assembly in response to thehigh-pressure boundary and the low-pressure boundary. When pressurelocked, the net effect of the pressure forces from the high-pressureboundary and the low-pressure boundary may be used to maintain theconfiguration, and accordingly maintain the seal, of the ring segmentsand at least one gap covers. For example, during operation, if gap coverelement 412 were perturbed to move radially inward (e.g., and lose, orstart to lose, engagement), the net pressure forces would act to restoregap cover element 412 to sealing against the wedge recess.

In a further example of pressure locking, considering each of gap coverelements 472, 474, 476, and 478 during operation, the radially inwardsurface of each is larger than the corresponding radially outwardsurface. Also, the pressure at each radially inward surface isindicative of a high-pressure region, while the pressure at eachradially outward surface is equal to or less than this pressure.Accordingly, the resultant radial force from pressure forces on each ofgap cover elements 472, 474, 476, and 478 may be directed radiallyoutward, thus aiding in maintaining the relative positions of gap coverelements 472, 474, 476, and 478, first ring segments 462, 464, 466, and468, and second ring segments 463, 465, 467, and 469.

In a further example of pressure locking, considering each of secondring segments 463, 465, 467, and 469 during operation, the axiallyforward surface of each exposed to high-pressure gas is larger than thecorresponding axially rearward surface exposed to high pressure gas(e.g., that is not covered/sealed by a gap cover element or first ringsegment). Also, the pressure at each axially forward surface isindicative of a high-pressure region, while the pressure at each axiallyrearward surface is equal to or less than this pressure. Accordingly,the resultant axial force from pressure forces on each of second ringsegments 463, 465, 467, and 469 may be directed axially rearward, thusaiding in maintaining the relative positions of gap cover elements 472,474, 476, and 478, first ring segments 462, 464, 466, and 468, andsecond ring segments 463, 465, 467, and 469.

In some embodiments, sealing ring assembly 400 may be include asolid-lubricant material such as, for example, graphite. For example, afirst ring may be machined from graphite, and split into first ringsegments 402, 404, 406, and 408. In a further example, first ringsegments 402, 404, 406, and 408 may be machined as separate parts. Inanother further example, first ring segments 402, 404, 406, and 408 maybe machined from graphite as separate parts. In another example, sealingring assembly 400 may be machined from graphite as a single ring, andthen further machined (e.g., wire or laser cut) into first ring segments402, 404, 406, 408, second ring segments 403, 405, 407, and 409, andinto gap cover elements 412, 414, 416, and 418.

As first ring segments 402, 404, 406, and 408 wear, they move outwardand the splits at the interfaces open wider (e.g., shown illustrativelyby corresponding first ring segments 432, 434, 436, and 438). Gap coverelements 472, 474, 476, and 478 are pressed outward by gas pressure andwear in the radial direction while being supported by the angled sidesof the respective wedge recesses. Accordingly, the wear rates of gapcover elements 472, 474, 476, and 478 may be self-adjusting to maintaincontact with both the angled sides of the wedge recess and the cylinderinner surface (e.g., the bore). In some circumstances, gap coverelements may wear at a faster rate than the corresponding ring segments,and the wear rate may depend on the wedge angle. Because gap coverelements 472, 474, 476, and 478 maintain contact with the angled sidesof the respective wedge recesses, as well as the bore, sealingperformance may be maintained throughout the life of operation (e.g., asthe ring wears). Further, there are no significant gaps between the ringsegments and corresponding gap cover elements exposed to a low-pressureboundary of the sealing ring assembly. The ring segment is supportedeverywhere either by pressure or by the wedge, avoiding the stressscenario described in the context of FIG. 3.

FIG. 12 shows a view of the front face of illustrative sealing ringassembly 500 at a new or low wear condition, with second ring segment503 removed, in accordance with some embodiments of the presentdisclosure. Illustrative sealing ring assembly 500, as shown, is similarto sealing ring assembly 400, for example. FIG. 13 shows a view of therear face of illustrative sealing ring assembly 500 at a new or low wearcondition, with second ring segment 503 removed, in accordance with someembodiments of the present disclosure. Second ring segment 509 is shownin place, for reference. Gap cover element 512 engages the wedge recessin interface 520 where first ring segments 502 and 508 meet. Interface520 includes an axially-through wedge recess.

FIG. 14 shows a view of the rear face of an illustrative sealing ringassembly 600 at a new or low wear condition, in accordance with someembodiments of the present disclosure. Sealing ring assembly 600includes ring segments 602, 604, 606, and 608, as well as gap coverelements 612, 614, 616, and 618. Sealing ring assembly 600 includes fourring segments and four gap cover element, although any suitable numberof ring segments and corresponding gap cover elements may be used inaccordance with the present disclosure.

FIG. 15 shows a view of the rear face of an illustrative sealing ringassembly 630 at a high wear condition, in accordance with someembodiments of the present disclosure. Sealing ring assembly 630includes ring segments 632, 634, 636, and 638, as well as gap coverelements 642, 644, 646, and 648. Sealing ring assembly 630illustratively corresponds to sealing ring assembly 600 after undergoinghigh wear (e.g., ring segment 636 corresponds to ring segment 606 afterundergoing high wear).

FIG. 16 shows a view of the rear face of an illustrative sealing ringassembly 660 at an intermediate wear condition, in accordance with someembodiments of the present disclosure. Sealing ring assembly 660includes ring segments 662, 664, 666, and 668, as well as gap coverelements 672, 674, 676, and 678. Sealing ring assembly 660illustratively corresponds to sealing ring assembly 600 after undergoingless wear than sealing ring assembly 630 wear (e.g., ring segment 666corresponds to ring segment 606 after undergoing intermediate wear).

The following discussion is described in the context of FIGS. 14-16 todescribe the sealing ring assembly, behavior thereof, and wear thereof.For purposes of discussion, FIGS. 14-16 may be described as views of anillustrative sealing ring assembly at different stages of wear life.Accordingly, for purposes of clarity any of FIGS. 14-16 may bereferenced to describe features of an illustrative sealing ringassembly. Geometrical directions are referred to herein in terms ofcylindrical coordinates for simplicity (e.g., X is the axial direction,R is the radial direction and θ is the azimuthal direction, as shown inFIG. 14). It will also be understood that any of sealing ring assemblies600, 630, and 660 may represent a sealing ring assembly in a newcondition. For example, a sealing ring assembly may be newly createdthat resembles sealing ring assembly 630 (e.g., with significant gapsbetween gap cover elements on a high-pressure boundary).

Ring segments 602, 604, 606, and 608 may move radially outward tomaintain sealing contact with the inner surface of the bore of acylinder as ring material is removed via wear. Sealing ring assembly 600may be energized radially outward against the cylinder bore by thepresence of gas pressure (e.g., from a relatively high-pressure portionof an engine cycle or air compression cycle) on the inner surface ofsealing ring assembly 600.

Sealing ring assembly 600 includes four interfaces between adjacent ringsegments. For example, there are respective interfaces between ringsegments 602 and 604, ring segments 604 and 606, ring segments 606 and608, and ring segments 608 and 602. The interfaces of sealing ringassembly 600 form respective wedge recesses, centered at each of theinterfaces. A wedge recess is, for example, the space where wedge-shapedgap cover element 612 fits, as shown in FIG. 14. As shown in FIGS.14-16, the wedge recesses each extend through the entire radial sectionof the corresponding ring segments (e.g., from radially inward surfacethrough radially outward surface), and the entire axial section of thering segments. As shown in FIGS. 15 and 16, the sides of the wedgerecesses are symmetric about a plane passing through the center of theradial split in the ring. The sides together form a wedge angle that iswidest at the radially inner surface of the ring segments and narrowestat the radially outer surface.

Gap cover elements 612, 614, 616, and 618 include respective wedges, andfit into corresponding wedge recesses formed in interfaces betweenadjacent ring segments (e.g., ring segments 602 and 604). Gap coverelements fitted into each of the corresponding recesses, may form a sealwith no gaps. The gap cover elements are acted upon by gas pressure onthe radially inner surface, exerting a force radially outward. Forexample, during high pressure portions of an engine cycle or aircompressor cycle, high gas pressure may act on the radially innersurfaces of gap cover elements 612, 614, 616, and 618. This high gaspressure forces the angled sides of each gap cover element against thecorresponding angled sides of the respective wedge recess, creating aseal against radial gas leakage through the interface. Also, when actedon by high gas pressure at the radially inward surface, the radiallyoutward surface of the gap cover element presses against the innersurface of the cylinder (e.g., the bore), forming a seal against axialleakage through the interface, past the sealing ring assembly.

In some embodiments, sealing ring assembly 600 may be include asolid-lubricant material such as, for example, graphite.

As ring segments 602, 604, 606, and 608 wear they move outward and thesplits open wider (e.g., shown illustratively by corresponding ringsegments 632, 634, 636, and 638). Gap cover elements 662, 664, 666, and668 are pressed outward by gas pressure and wear in the radial directionwhile being supported by the angled sides of the respective wedgerecesses. Accordingly, the wedge wear rate may be self-adjusting tomaintain contact with both the angled sides of the wedge recess and thecylinder inner surface (e.g., the bore). In some circumstances, gapcover elements may wear at a faster rate than the corresponding ringsegments, and wear rate may depend on the wedge angle. In somecircumstances, ring segments may wear at the same rate as, or a fasterrate than, the corresponding gap cover elements. Because the gap coverelements maintain contact with the angled sides of the respective wedgerecesses, as well as the bore, sealing performance may be maintainedthroughout the life of operation (e.g., as sealing ring 600 wears).Further, there are no significant gaps between the ring segments and gapcover elements exposed to a low-pressure boundary of sealing ringassembly 600. Each ring segment is supported everywhere either bypressure or by the piston, avoiding the stress scenario described in thecontext of FIG. 3.

FIG. 17 shows a view of the front face of illustrative sealing ringassembly 700 at a new or low wear condition, with ring segment 702removed, in accordance with some embodiments of the present disclosure.Illustrative sealing ring assembly 700, as shown, is similar to ringassembly 600, for example. FIG. 18 shows a view of the rear face ofillustrative sealing ring assembly 700 at a new or low wear condition,with ring segment 702 removed, in accordance with some embodiments ofthe present disclosure. Ring segment 704 is shown in place, forreference. It will be understood that sealing ring assembly 700, asshown, includes gap cover elements 712 and 718 that are larger (e.g.,more volume, and more mass if of the same material) than ring segments702 and 704. It will be understood that gap cover elements and ringsegments may be of any suitable relative sizes (e.g., thicknesses,widths, areas, volumes), masses, or both.

FIG. 19 shows illustrative piston assembly 800 including sealing ringassembly 810, in accordance with some embodiments of the presentdisclosure.

Piston assembly 800 includes piston 802, onto which sealing ringassembly 810 is arranged. For example, piston 802 may include a ringgroove into which sealing ring assembly 810 fits. Piston assembly 800may be configured to translate along axis 812. In some embodiments,piston 802 may be an open-faced piston. In some embodiments, piston 802may include more than one ring groove to accommodate more than onerespective sealing ring assembly. In some embodiments, piston 802 mayinclude an integrated gap cover feature. For example, a ring may includeone or more ring segments having one or more corresponding interfaces. Apiston may include an integrated gap cover feature arranged at any ofthe one or more interfaces. In an illustrate example, a ring may includefour ring segments having four interfaces, for which wedge-shaped gapcover elements are included at two interfaces, and piston-integrated gapcover features are included at the other two interfaces.

FIG. 20 shows a cross section view of illustrative piston and cylinderassembly 900 including sealing ring assembly 920, in accordance withsome embodiments of the present disclosure. Cylinder 960 may includebore 962, which is the inner cylindrical surface in which pistonassembly 910 travels. Piston assembly 910 may include piston 926, whichincludes a sealing ring groove 922, in which sealing ring assembly 920is configured to ride. As piston assembly 910 translates along the Xdirection (e.g., during an engine cycle), in cylinder 960, the gaspressure in high pressure region 950 may change (high pressure region950 may be closed with a cylinder head or an opposing piston). Forexample, as piston assembly 910 moves in the negative X direction (i.e.,to the left in FIG. 20), the pressure in high pressure region mayincrease. Low pressure region 970, located to the rear of the sealingring assembly may be at a gas pressure below the pressure of highpressure region 950 for at least some, if not most, of a stroke or cycleof piston and cylinder assembly 900. The pressure ranges inhigh-pressure region 950 and low-pressure region 970 may be any suitableranges (e.g., sub-atmospheric pressure to well over 250 bar), and maydepend on compression ratio, engine breathing details (e.g., boostpressure, pressure waves, port timing), losses, thermochemicalproperties of gases, and reaction thereof. Accordingly, the sealing ringassemblies described herein may be used to seal any suitablehigh-pressure region and low-pressure region, having any suitablepressure ranges. For example, in some embodiments, low pressure region970 may interact flow-wise with intake or exhaust ducting, and bemaintained relatively near pressure in the ducting. In an illustrativeexample, low pressure region 970 may open to intake breathing ports, andmay be at a pressure near to or strongly affected by (e.g., on average)an intake pressure (e.g., a boost pressure). In a further illustrativeexample, low pressure region 970 may open to exhaust breathing ports,and may be at a pressure near to or strongly affected by (e.g., onaverage) an exhaust pressure. In accordance with the present disclosure,sealing ring assemblies may be used to seal high pressure regions fromlow pressure regions for at least part of a stroke or cycle of a pistonand cylinder assembly. It will be understood that the “front” of sealingring assembly 920 refers to the face axially nearest high-pressureregion 950, and the “rear” of sealing ring assembly 920 refers to theface axially nearest low-pressure region 970.

It will be understood that unless otherwise specified, all pressuresreferred to herein are in absolute units (e.g., not gage or relative).

It will be understood that high-pressure and low-pressure may refer totransient pressure states of a piston and cylinder device. For example,referencing an engine cycle, the high-pressure side of a sealing ringassembly may have a pressure greater than a low-pressure side of thesealing ring assembly for most of the engine cycle (e.g., exceptpossibly during breathing or near-breathing portions of the cycle).Accordingly, high-pressure and low pressure are relative and depend onthe conditions of the gas being sealed.

A sealing ring assembly may be used to seal a high pressure and alow-pressure region, each operating in any suitable pressure range. Itwill also be understood that a sealing ring assembly may sealdifferently at different positions in a cycle. It will be furtherunderstood that a low-pressure region may include a pressure greaterthan a pressure of a high-pressure region for some of a piston stroke orcycle of a piston and cylinder assembly. For example, a sealing ringassembly may always seal a high-pressure region from a low-pressureregion. In a further example, a sealing ring assembly may seal ahigh-pressure region from a low-pressure region as long as the pressurein the high-pressure region is greater than the pressure in thelow-pressure region. In a further example, a sealing ring assembly mayseal a high-pressure region from a low-pressure region as long as thepressure in the high-pressure region is greater than the pressure in thelow-pressure region, and conversely, seal a low-pressure region from ahigh-pressure region as long as the pressure in the low-pressure regionis greater than the pressure in the high-pressure region.

In some embodiments, sealing ring assembly 920 may deposit material onbore 962 of cylinder 960 (e.g., include a self-lubricating material).Deposited material may lubricate the bore-to-sealing ring assemblyinterface between bore 962 and sealing ring assembly 920 (e.g., providea dry lubricant). Accordingly, in some embodiments, piston and cylinderassembly 900 may operate without liquid for lubrication (e.g., oil).

In some embodiments, piston 926 may be an open-faced piston. Forexample, piston 926 may include openings, cutouts, or other fluid pathsfrom high-pressure region 950 to ring groove 922. Accordingly, in someembodiments employing an open-faced piston, the radially inward surfaces(e.g., referencing radial direction R in FIG. 20) of sealing ringassembly 920 may be exposed to gas pressure of high pressure region 950.

FIG. 21 shows a cross-sectional view of illustrative device 1000including two free piston assemblies 1010 and 1020 that includerespective sealing ring assemblies 1012 and 1022 in accordance with someembodiments of the present disclosure. In some embodiments, device 1000may include linear electromagnetic machines 1050 and 1055 to convertbetween kinetic energy of respective free piston assemblies 1010 and1020 and electrical energy. In some embodiments, device 1000 may includegas regions 1060 and 1062, which may, for example, be at a relativelylower pressure than gas region 1070 (e.g., a high-pressure region) forat least some, if not most, of a cycle (e.g., an engine cycle, or an aircompression cycle). For example, gas regions 1060 and 1062 (e.g., lowpressure regions) may be open to respective breathing ducting (e.g., anintake manifold, an intake system, an exhaust manifold, an exhaustsystem). To illustrate, breathing ports 1034 and 1035 are configured toprovide reactants to, and remove exhaust from, bore 1032 of cylinder1030. In a further example, gas regions 1060 and 1062 may be vented toatmosphere (e.g., be at about 1.01 bar absolute pressure). In someembodiments, device 1000 may include gas springs 1080 and 1085, whichmay be used to store and release energy during a cycle in the form ofcompressed gas (e.g., a driver section). For example, free pistonassemblies 1010 and 1020 may each include respective pistons 1082 and1087, having grooves for respective sealing ring assemblies 1081 and1086, to seal respective gas regions 1083 and 1088 (e.g., high-pressureregions) from respective gas regions 1084 and 1089 (e.g., low-pressureregions).

Cylinder 1030 may include bore 1032, centered about axis 1072. In someembodiments, free piston assemblies 1010 and 1020 may translate alongaxis 1072, within bore 1032, allowing gas region 1070 to compress andexpand. For example, gas region 1070 may be at relatively high pressureas compared to gas region 1060 for at least some of a stroke of freepiston assemblies 1010 and 1020 (e.g., which may translate along axis1072 in opposed piston synchronization). Sealing ring assemblies 1012and 1022 may seal gas region 1070 from respective gas regions 1060 and1062 within bore 1032. In some embodiments, free piston assemblies 1010and 1020 may include respective pistons 1014 and 1024, and respectivesealing ring assemblies 1012 and 1022 which may be arranged inrespective corresponding grooves of pistons 1014 and 1024. It will beunderstood that gas regions 1060 and 1062, and gas region 1070, maychange volume as free piston assemblies 1010 and 1020 move or areotherwise positioned at different locations along axis 1072. Theportions of respective sealing ring assemblies 1012 and 1022 nearest gasregion 1070 are each termed the front, and the portion of sealing ringassemblies 1012 and 1022 nearest respective gas regions 1060 and 1062are each termed the rear. Sealing ring assemblies 1012 and 1022 may eachinclude a high-pressure boundary, which may each depend on a pressure ingas region 1070. For example, a high-pressure boundary of sealing ringassembly 1012 may be open to gas region 1070 (e.g., coupled by one ormore orifices, or other opening), and have a corresponding pressure thesame as (e.g., if gas from gas region 1070 is unthrottled in the sealingring assembly), or less than (e.g., if gas from gas region 1070 isthrottled in the sealing ring assembly), the pressure of gas region1070. Sealing ring assemblies 1012 and 1022 may each include alow-pressure boundary, which may depend on a gas pressure in respectivegas regions 1060 and 1062. For example, a low-pressure boundary ofsealing ring assembly 1012 may be open to gas region 1060 and have acorresponding pressure about the same as the pressure of gas region1060.

In some embodiments, pistons 1014 and 1024 may each include one or moregrooves into which one or more respective sealing ring assemblies may bearranged. For example, as shown in FIG. 10, pistons 1014 and 1024 mayeach include one groove, into which sealing ring assembly 1012 andsealing ring assembly 1022 may be installed, respectively. In a furtherexample, although not shown in FIG. 21, piston 1014 may include twogrooves, in which two respective sealing ring assemblies may beinstalled. In a further example, piston 1014 may include two grooves,the first sealing ring assembly 1012, and the second (not shown),arranged to the rear of sealing ring assembly 1012, but with its frontnearer to gas region 1060, thereby sealing pressure in gas region 1060to pressure between the two sealing ring assemblies (e.g., which may beless than pressure in gas region 1070). Accordingly, a sealing ringassembly may be used to seal any suitable high pressure and low-pressureregions from each other.

In some embodiments, free piston assemblies 1010 and 1020 may includerespective magnet sections 1051 and 1056, which interact with respectivestators 1052 and 1057 to form respective linear electromagnetic machines1050 and 1055. For example, as free piston assembly 1010 translatesalong axis 1072 (e.g., during a stroke of an engine cycle), magnetsection 1051 may induce current in windings of stator 1052. Further,current may be supplied to respective phase windings of stator 1052 togenerate an electromagnetic force on free piston assembly 1010 (e.g., toeffect motion of free piston assembly 1010).

In some embodiments, pistons 1014 and 1024, sealing ring assemblies 1012and 1022, and cylinder 1030 may be considered a piston and cylinderassembly.

In some embodiments, device 1000 may be an engine, an air compressor,any other suitable device having a piston and cylinder assembly, or anycombination thereof. In some embodiments, device 1000 need not includetwo free piston assemblies. For example, cylinder 1030 could be closed(e.g., with a cylinder head), and free piston assembly 1010 alone maytranslate along axis 1072.

FIG. 22 shows an exploded perspective view of illustrative sealing ringassembly 2200, in accordance with some embodiments of the presentdisclosure. Sealing ring assembly 2200 includes first ring 2220, secondring 2230, and gap cover element 2236. First ring 2220 includes firstring segments 2222 and 2224, which meet at interfaces 2225 and 2226(e.g., there may be but need not be a gap). Second ring 2230 includessecond ring segments 2232 and 2234, which include interfaces 2235 (e.g.,flat planar interface) and 2236 (e.g., a wedge-shaped recess).Interfaces 2225 and 2226 do not align azimuthally with interfaces 2235and 2236, thus preventing an axial leak path through azimuthally-alignedinterfaces. Radially outside surface 2202 of second ring 2230 isconfigured to contact a corresponding integrated gap cover feature of apiston during operation, during assembly, when assembled, or acombination thereof. Although shown as extending azimuthally fully, orvery nearly fully, 360 degrees, first ring 2220 need not extend the fullcircumference. For example, a first ring may include ring segmentsextending azimuthally just sufficient to cover a split in the secondring (e.g., a first ring may include ring segments with relatively largeazimuthal gaps at the interfaces). During operation (e.g., sealing ahigh-pressure region from a low-pressure region), first ring 2220 isconfigured to seal axially against second ring 2230 and gap coverelement 2236, as well as a bore of a cylinder. Second ring 2230 isconfigured to seal against a ring groove of a piston, apiston-integrated gap cover feature, gap cover element 2236, first ring2220, and the bore.

FIG. 23 shows a cross-sectional view (e.g., though a ring groove ofpiston 2310) of a portion of illustrative piston 2310, with a sealingring assembly disassembled, in accordance with some embodiments of thepresent disclosure. The sealing ring assembly of FIG. 23 is similar tosealing ring assembly 2200 of FIG. 22, for example. Ring segments 2322and 2324 constitute a first ring, ring segments 2332 and 2334 constitutea second ring. Gap cover element 2340 interfaces to ring segments 2332and 2334 in the ring groove of piston 2310. The first ring is removedfrom the second ring in FIG. 23 for clarity. The first ring includesinterfaces 2325 and 2326, that do not align azimuthally with interfacesof the second ring. Ring segments 2332 and 2334 are configured to sealagainst piston-integrated gap cover feature 2312. Ring segment 2324 isconfigured to seal axially against gap cover feature 2312. As shownillustratively in FIG. 23, gap-cover feature 2312 includes a circlesegment-shaped cross section. For example, the boundary of the circlesegment-shaped cross section includes a chord extending between twopoints on an outer radial surface of piston 2310, and an arc along theouter radial surface of piston 2310. A gap-cover feature may include anysuitable cross-sectional shape, which may contact a section of a secondring, in accordance with the present disclosure.

A gap-cover feature (e.g., having a flat surface or otherwise) isrigidly attached to, or are part of, the piston when assembled (e.g.,and do not move relative to the piston). In some embodiments, agap-cover feature is a contiguous part of the piston such as, forexample, a feature left over from machining or casting a ring grooveinto a piston billet. In some embodiments, a gap-cover feature issecured (i.e., affixed) to a piston using, for example, an adhesive, aweld (e.g., an ultrasonic weld, or a TiG weld), a braze joint, afastener (e.g., via engaging mating threads), a pin (e.g., via pressfitting), an interlocking interface, any other suitable securement, orany combination thereof. In an illustrative example, one or moregap-cover features may be retrofitted onto a piston of the prior art(e.g., along with any suitable modifications to a ring groove or pistonface) in accordance with the present disclosure. In a furtherillustrative example, a piston may be created from one or morecomponents, and one or more gap-cover features may be part of the one ormore components, or components themselves.

It will be understood that the present disclosure is not limited to theembodiments described herein and can be implemented in the context ofany suitable system. In some suitable embodiments, the presentdisclosure is applicable to reciprocating engines and compressors. Insome embodiments, the present disclosure is applicable to free-pistonengines and compressors. In some embodiments, the present disclosure isapplicable to combustion and reaction devices such as a reciprocatingengine and a free-piston engine. In some embodiments, the presentdisclosure is applicable to non-combustion and non-reaction devices suchas reciprocating compressors and free-piston compressors. In someembodiments, the present disclosure is applicable to gas springs. Insome embodiments, the present disclosure is applicable to oil-freereciprocating and free-piston engines and compressors. In someembodiments, the present disclosure is applicable to oil-freefree-piston engines with internal or external combustion or reactions.In some embodiments, the present disclosure is applicable to oil-freefree-piston engines that operate with compression ignition, chemicalignition (e.g., exposure to a catalytic surface, hypergolic ignition),plasma ignition (e.g., spark ignition), thermal ignition, any othersuitable energy source for ignition, or any combination thereof. In someembodiments, the present disclosure is applicable to oil-freefree-piston engines that operate with gaseous fuels, liquid fuels, orboth. In some embodiments, the present disclosure is applicable tolinear free-piston engines. In some embodiments, the present disclosureis applicable to engines that can be combustion engines with internalcombustion/reaction or any type of heat engine with external heataddition (e.g., from a heat source or external reaction such ascombustion).

The foregoing is merely illustrative of the principles of thisdisclosure and various modifications may be made by those skilled in theart without departing from the scope of this disclosure. The abovedescribed embodiments are presented for purposes of illustration and notof limitation. The present disclosure also can take many forms otherthan those explicitly described herein. Accordingly, it is emphasizedthat this disclosure is not limited to the explicitly disclosed methods,systems, and apparatuses, but is intended to include variations to andmodifications thereof, which are within the spirit of the followingclaims.

What is claimed is:
 1. A sealing ring assembly, comprising; a ringcomprising a first end face and a second end face defining an interface,at least one of the first and second end faces at least partially facingradially inward, wherein the ring is configured to cause the interfaceto widen as the ring wears; and a gap cover element configured to form aseal against the first and second end faces, wherein the gap coverelement is configured to move radially outward to maintain the seal asthe interface widens.
 2. The sealing ring assembly of claim 1, whereinthe ring comprises a radially outer surface configured to seal against abore; the gap cover element comprises a radially outer surfaceconfigured to seal against the bore as the ring wears; and as theinterface widens, at least some of the radially outer surface of the gapcover element is configured to widen.
 3. The sealing ring assembly ofclaim 1, wherein the first and second end faces form a wedge-shapedrecess and wherein the gap cover element comprises a wedge configured toengage with the wedge-shaped recess.
 4. The sealing ring assembly ofclaim 1, wherein the ring comprises a back face configured to be incontact with a low-pressure region, and wherein the gap cover element isconfigured to form the seal with the first and second end faces adjacentto the back face.
 5. The sealing ring assembly of claim 1, wherein thering is a first ring, and further comprising a second ring comprising atleast one ring segment arranged axially adjacent to the first ring andconfigured to seal axially against the first ring and against the gapcover element.
 6. The sealing ring assembly of claim 1, wherein at leastone of the ring and the one gap cover element are comprised of arespective self-lubricating material.
 7. The sealing ring assembly ofclaim 1, wherein the ring and the gap cover element are configured tooperate without a liquid lubricant.
 8. The sealing ring assembly ofclaim 1, wherein: the interface is a first interface; the gap coverelement is a first gap cover element; the ring comprises a third endface and a fourth end face defining a second interface, each of thethird and fourth end faces at least partially facing radially inward,wherein the ring is configured to cause the second interface to widen asthe ring wears; the sealing ring assembly further comprises a second gapcover element configured to form a second seal against the third andfourth end faces; and the second gap cover element is configured to moveradially outward to maintain the second seal as the second interfacewidens.
 9. The sealing ring assembly of claim 8, wherein the ringcomprises at least two ring segments.
 10. The sealing ring assembly ofclaim 1, wherein: the ring further comprises a first axial end face anda second axial end face further defining the interface; and the gapcover element is further configured to seal against the first and secondaxial end faces.
 11. The sealing ring assembly of claim 1, wherein theat least one of the first and second end faces comprises an azimuthalcomponent and a radial component.
 12. A piston assembly, comprising: apiston comprising a circumferential groove that extends around an outersurface of the piston; and a sealing ring assembly arranged in thecircumferential groove, the sealing ring assembly comprising: a ringcomprising a first end face and a second end face defining an interface,at least one of the first and second end faces at least partially facingradially inward, wherein the ring is configured to cause the interfaceto widen as the ring wears, and a gap cover element configured to form aseal against the first and second end faces, wherein the gap coverelement is configured to move radially outward to maintain the seal asthe interface widens.
 13. The piston assembly of claim 12, wherein: thering comprises a radially outer surface configured to seal against abore; the gap cover element comprises a radially outer surfaceconfigured to seal against the bore as the ring wears; and as theinterface widens, at least some of the radially outer surface of the gapcover element is configured to widen.
 14. The piston assembly of claim12, wherein the first and second end faces form a wedge-shaped recessand wherein the gap cover element comprises a wedge configured to engagewith the wedge-shaped recess.
 15. The piston assembly of claim 12,wherein the ring comprises a back face configured to be in contact witha low-pressure region, and wherein the gap cover element is configuredto form the seal with the first and second end faces adjacent to theback face.
 16. The piston assembly of claim 12, wherein the ring is afirst ring, and further comprising a second ring comprising at least onering segment arranged axially adjacent to the first ring and configuredto seal axially against the first ring and against the gap coverelement.
 17. The piston assembly of claim 12, wherein at least one ofthe ring and the one gap cover element are comprised of a respectiveself-lubricating material.
 18. The piston assembly of claim 12, whereinthe ring and the gap cover element are configured to operate without aliquid lubricant.
 19. The piston assembly of claim 12, wherein: theinterface is a first interface; the gap cover element is a first gapcover element; the ring comprises a third end face and a fourth end facedefining a second interface, each of the third and fourth end faces atleast partially facing radially inward, wherein the ring is configuredto cause the second interface to widen as the ring wears; the sealingring assembly further comprises a second gap cover element configured toform a second seal against the third and fourth end faces; and thesecond gap cover element is configured to move radially outward tomaintain the second seal as the second interface widens.
 20. The pistonassembly of claim 19, wherein the ring comprises at least two ringsegments.
 21. The piston assembly of claim 12, wherein: the ring furthercomprises a first axial end face and a second axial end face furtherdefining the interface; and the gap cover element is further configuredto seal against the first and second axial end faces.
 22. The pistonassembly of claim 12, wherein the at least one of the first and secondend faces comprises an azimuthal component and a radial component.
 23. Adevice comprising: a cylinder comprising a bore; a piston comprising acircumferential groove that extends around an outer surface of thepiston, wherein the piston is configured to translate axially in thebore; and a sealing ring assembly arranged in the circumferentialgroove, wherein the sealing ring assembly is configured to seal againstthe bore, the sealing ring assembly comprising: a ring comprising afirst end face and a second end face defining an interface, at least oneof the first and second end faces at least partially facing radiallyinward, wherein the ring is configured to cause the interface to widenas the ring wears; and a gap cover element configured to form a sealagainst the first and second end faces, wherein the gap cover element isconfigured to move radially outward to maintain the seal as theinterface widens.
 24. The device of claim 23, wherein: the ringcomprises a radially outer surface configured to seal against the bore;the gap cover element comprises a radially outer surface configured toseal against the bore as the ring wears; and as the interface widens, atleast some of the radially outer surface of the gap cover element isconfigured to widen.
 25. The device of claim 23, wherein the first andsecond end faces form a wedge-shaped recess and wherein the gap coverelement comprises a wedge configured to engage with the wedge-shapedrecess.
 26. The device of claim 23, wherein the bore comprises alow-pressure region, wherein the ring comprises a back face configuredto be in contact with the low-pressure region, and wherein the gap coverelement is configured to form the seal with the first and second endfaces adjacent to the back face.
 27. The device of claim 23, wherein thering is a first ring, and further comprising a second ring comprising atleast one ring segment arranged axially adjacent to the first ring andconfigured to seal axially against the first ring and against the gapcover element.
 28. The device of claim 23, wherein at least one of thering and the one gap cover element are comprised of a respectiveself-lubricating material.
 29. The device of claim 23, wherein the ringand the gap cover element are configured to operate without a liquidlubricant.
 30. The device of claim 23, wherein the at least one of thefirst and second end faces comprises an azimuthal component and a radialcomponent.